Plastics film, use of dyestuffs therein and process for testing the authenticity of packaged goods

ABSTRACT

A dyestuff capable of undergoing a clearly visible colour change when contacted with a color-developing material is dispersed in the body of a plastics film and used in the identification of goods. The film can be used for packaging of the goods or as a label or seal affixed to the goods. When testing the authenticity of packaging goods, the plastics film is marked with the color-developing chemical to produce a colored mark on the package. The dyestuff is preferably a latent dyestuff which is colorless and invisible to the eye under ambient conditions for use of the film but which forms a clearly visible color when contacted with the color-developing material.

FIELD OF THE INVENTION

This invention relates to plastics film useful for packaging or forlamination to paper or board to form packaging or promotional materialand to the preparation and use of such film. In particular, it relatesto plastics film useful for security packaging having a feature which isnot apparent to the eye but which can readily be revealed in a test forauthenticity. It also relates to the use in the identification of goodsof dyestuffs capable of undergoing a clearly visible colour change whencontacted with a colour-developing material and to a process for testingthe authenticity of packaged goods.

BACKGROUND ART

Invisible inks have long been known and have been used or suggested foruse in various covert marking procedures. For example, U.S. Pat. No.5,424,266, U.S. Pat. No. 5,476,830 and U.S. Pat. No. 5,532,200 describea latent image printing method and apparatus in which a substrate withone main surface has a covering comprising a dye defining a backgroundcolour. When the dye is mixed with a colour developer they produce aspectral response which is visible relative to the background colour.There is a continuous coating over the covering which is non-porous andsolvent-resistant with respect to the colour developer. U.S. Pat. No.5,421,809 and U.S. Pat. No. 5,516,362 describe a security marking methodcomprising marking a portion of a substrate by applying a first markingfluid which is invisible when illuminated by both visible light andultraviolet light and activating the marked portion by applying a secondmarking fluid thereon. The second marking fluid is reactable with thefirst marking fluid to be invisible when illuminated by visible lightand fluorescent when illuminated by ultraviolet light.

U.S. Pat. No. 5,595,590 describes a method for authenticating a documentor article comprising applying a mixture of a carrier, a leuco dye andan activator to a surface of a document or article, wherein the leucodye and activator react in response to a rubbing force applied to thesurface so as to change colour.

GB-A-1593172 describes an apparatus for applying written or drawninformation onto image carriers for overhead projectors, comprising animage carrier in film or plate form which includes at least one colouredcompound, as well as a writing or drawing marker, the writing or drawingfluid of which contains at least one colourless compound. Thiscolourless compound reacts with the coloured compound to produce acolour change.

DISCLOSURE OF THE INVENTION

We have found that a dyestuff capable of undergoing a clearly visiblecolour change when contacted with a colour-developing chemical is usefulin the identification or authentication of goods when it is dispersed inthe body of a plastics film.

The plastics film can be used in packaging goods, generally as theoutermost layer of packaging over at least part of the surface area ofthe packaged goods or in a position such that it can easily be contactedby the colour-developing chemical. The plastics film can be used as alabel or seal affixed to goods, for example a seal which has to bebroken to open the package. The plastics film can be used as theouter(most) layer of laminated packaging.

The invention also includes a process for testing the authenticity ofpackaged goods, characterised in that the goods are packaged inpackaging material including a plastics film having a dyestuff dispersedin the body of the plastics film, said dyestuff being capable ofundergoing a clearly visible colour change when contacted with acolour-developing chemical, and the said plastics film is marked withthe colour-developing chemical to produce a coloured mark on thepackage.

The invention also includes a plastics film having a dyestuff dispersedin the body of the plastics film, characterised in that the dyestuff isa latent dyestuff which is colourless and invisible to the eye underambient conditions for use of the film but which forms a clearly visiblecolour when contacted with a colour-developing chemical.

The system of the present invention has the advantage over invisible inksecurity marking systems of being more difficult to replicate, and hencemore secure, and also more durable whilst being just as easy to markwhen testing for authenticity. The dyestuff is distributed throughoutthe film, which is a self-supporting film, rather than simply beingprinted on the surface, and access to the film can be restricted toreputable manufacturers, for example manufacturers of expensive brandedluxury goods and products or compact discs or computer software. Filmhaving an area printed with invisible ink is often detectable because aslight difference of gloss in the printed area is visible, whereasdispersion of the dyestuff in the body of the film in accordance withthe invention does not indicate to a counterfeiter that the dyestuffacts as a security check.

The plastics film can for example be a cast film such as a castcellulose acetate film or can be an extruded film such as a polyolefinfilm, for example polyethylene or polypropylene, or a polyester film,for example polyethylene terephthalate. The film can be a clear, matt orsemi-matt film. The film can be crosslinked, for example crosslinkedcellulose acetate film. The film can contain any of the additives knownfor incorporation in film, provided that these do not obscure the colourdeveloped by the dyestuff and colour-developing chemical. Celluloseacetate film can for example contain a plasticiser, for example 10 to25% by weight of a phthalate ester plasticiser such as diethylphthalate. The thickness of the film is generally in the range 5 to 500microns, more usually 10 or 15 microns up to 50 or 100 microns. Forexample, film for lamination over print, e.g. for lamination overpaperboard packaging, may have a thickness of 10 to 25 or 40 microns andfilm for other uses such as labels and seals or for window packaging mayhave a thickness of 25 to 75 microns.

The dyestuff is preferably a latent dyestuff which is colourless andinvisible to the eye under ambient conditions for use of the film butwhich forms a clearly visible colour when contacted with acolour-developing chemical. The film can thus appear as an ordinarytransparent or translucent film in normal use. The dyestuff canalternatively form a coloured film under ambient conditions which ischanged to colourless or to a different colour by the colour-developingchemical.

The dyestuff can for example be an acid/base indicator, preferably alatent dyestuff indicator which is inconspicuous at ambient pH for useof the film (usually neutral pH) but which develops colour on contactwith strong acid or strong base. Phenolphthalein, for instance, iscolourless at neutral pH but develops a vivid pink colour when markedwith alkali, and thymolphthalein is colourless at neutral pH butdevelops a blue colour when marked with alkali. The colour developmentsystem is preferably reversible in most cases so that, after thecoloured mark has been observed, the marked area can be contacted with achemical which reacts with the dyestuff to change it back to itsoriginal colour, for example the colourless and invisible form of alatent dyestuff. As a result, the marked area is indistinguishable fromthe rest of the film. In other words, the packaged goods can beauthenticated but then sold unmarked. Acid/base indicators are generallyreversible. A pink mark on a film containing phenolphthalein will vanishwhen overmarked with an acid. The latent dyestuff can alternatively be aleuco dye. 4-Nitrophenol and 3-nitrophenol are examples of dyes whichchange colour on application of acid, being yellow at neutral pH andchanging to olive or green at acidic pH. The dyestuff incorporated inthe film can be a material sold commercially as a colour developer, withthe corresponding coupler being applied as the colour-developingchemical of the invention. For example, the material sold as “ColorDeveloper CD3” for use in coloured photographic film base, believed tobe a salt of3-methyl-N-(2-methylsulphonamido)ethyl-N-ethyl-p-phenylenediamine (CASNo 25646-71-3), can be incorporated in the film, with a coupler compoundsuch as that sold as “Yellow Coupler 2”, believed to be2-[4′-(4-benzyloxyphenylsulphonyl)phenoxy]N-2′chloro-5′-[4-(2,5-di-tertamylphenoxy)butyramido]phenyl-2-pivaloyl acetamide (CAS No. 30744-85-5),applied as a colour-developing chemical in conjunction with an oxidisingagent such as a peroxide. The yellow colour developed can be changedback to colourless by a reducing agent.

The invention includes a process for the preparation of a plastics film,in which a dyestuff capable of undergoing a clearly visible colourchange when contacted with a colour-developing chemical, preferably alatent dyestuff as described above, is dispersed in a film-formingplastics material and the plastics material is then converted into film.The amount of dyestuff incorporated in the film is preferably at least0.1 or 0.2% by weight up to 5 or 10% by weight, for example 0.5 to 2.0%by weight. The optimum amount of dyestuff varies according to theintensity of the dye in its colour-developed state.

Cast film is generally produced by casting a solution of film-formingplastics material onto an endless belt, which is a polished metal beltfor producing clear film. Matt or semi-matt film can be produced bycasting on a roughened belt or by embossing film with a roughenedroller. The dyestuff is preferably included in the casting solution. Itcan in many cases be directly dissolved in the solution. Celluloseacetate film, for example, is cast from acetone solution, and manydyestuffs (including most latent dyestuffs) are acetone-soluble.Alternatively, a solution of the dyestuffs can be injected into thesolution of plastics material before it is cast. The concentration ofdyestuff in the solution injected is greater than the requiredconcentration of dyestuff in the film and can for example be 5 to 75% byweight. The dyestuff solution is preferably a solution in the samesolvent as that used in the plastics material solution, although amiscible solvent can alternatively be used. The solution of plasticsmaterial generally passes through a set of static mixers or baffles justbefore the casting bar, and the dyestuff solution can for example beinjected just upstream of the static mixers.

The dyestuff can alternatively be added in liquid form, for example as asolution or dispersion, after casting, although it may be more difficultin this case to ensure that the latent dyestuff is dispersed throughoutthe body of the plastics film. The dyestuff solution can for example beadded just after casting, while the cast plastics material solution isstill liquid or contains a high residual level of casting solvent, orthe cast film can be further softened by the surface application ofadditional casting solvent, either as the solvent in which the dyestuffis applied or as a liquid applied to the film before the dyestuff isapplied. Solvent can for example be applied to the film by a lickroller, as described in EP-A-802069.

The film can alternatively be a melt-extruded film, in which case adispersion of the dyestuff in the film-forming plastics material, whichmay for example be a polyolefin such as polyethylene or polypropylene,or a polyester such as polyethylene terephthalate, is melt-extruded asfilm. The dyestuff can be dispersed direct in the plastics melt or asolution of the dyestuff, for example in a plasticiser for the film, canbe dispersed in the plastics melt, for example it can be injected intothe mixing stage of the extruder.

The plastics film is particularly suitable for laminating over printedpaperboard, for use in packaging. The laminated paperboard is generallyused with the film as its outer layer. The plastics film canalternatively be used as a packaging material without lamination or aswindow film in a window packaging. The film can be used, whether or notlaminated to a backing, as a label material, for example forpressure-sensitive labels and for seals.

The colour-developing chemical used to test for authenticity ispreferably held in a pen, for example a fibre tip pen, for easy use. Thecolour-developing chemical is preferably used in solution in a solventwhich does not damage the film. Where the colour development isreversible, the chemical for reversing colour is also preferably held ina second pen which can be applied over the area in which colour isdeveloped. For example, if the film contains an acid/base indicator suchas phenolphthalein, a first fibre tip pen contains an alkaline solutionto develop colour and a second fibre tip pen contains an acid solutionto remove colour.

The authentication process of the invention can be used in conjunctionwith other security features. For example, the film can have a regularembossed pattern of depth 0.5 to 10 microns and repeat distance 20 to400 microns whose regularity is sufficient for it to be capable ofgiving rise to a diffraction pattern or, as described in EP-A-802069, issuch that when the plastics film is rubbed it emits a noise ofcharacteristic frequency. The film can have different levels ofembossing in different areas of the film, for example different depthsand/or different repeat distance of embossing, to form a characterisingpattern such as the logo of the company whose products are packaged inthe film. The logo can be more or less highly embossed than the rest ofthe film or can be an unembossed area surrounded by embossed film orvice versa. The colour developing process can be applied totamper-evident film, for example to an embrittled film used fortamper-evident seals and labels such as crosslinked cellulose acetatefilm sold commercially under the Registered Trade Mark “Integuard”. Ahologram can be formed in the film containing a dyestuff by aconventional metallising and embossing process.

The invention is illustrated by the following Examples in which partsand percentages are by weight:

EXAMPLE 1

100 parts cellulose acetate, 20 parts diethyl phthalate and 20 partsphenolphthalein latent dyestuff were dissolved in acetone.

A solution of cellulose acetate and diethyl phthalate in acetone wasdegassed, passed through a set of static mixers and cast onto a polishedstainless steel belt. The dyestuff-containing solution described abovewas injected into the cellulose acetate solution just upstream of thestatic mixers. After evaporation of solvent, the clear film produced wasstripped from the belt and dried by passing it through a drying oven.The composition of the film produced was:

81.7% cellulose acetate

16.3% diethyl phthalate

2.0% phenolphthalein

The film was colourless.

A 0.033M aqueous solution of sodium hydroxide was mixed with an equalvolume of acetone and charged to a fibre tip pen. When the film wasmarked with this solution, a vivid pink colour rapidly developed.

A 0.033M aqueous solution of hydrochloric acid was mixed with an equalvolume of acetone. When this solution was applied to the pink-colouredmark, the coloured area rapidly decoloured.

EXAMPLE 2

The process of Example 1 was repeated using an equal weight ofthymolphthalein in place of the phenolphthalein. The same results wereobserved, except that the colour observed on marking with sodiumhydroxide solution was bright blue.

EXAMPLE 3

The process of Example 1 was repeated replacing half of thephenolphthalein by an equal weight of thymolphthalein. The same resultswere observed, except that the colour observed on marking with alkalisolution was lilac.

In both Examples 2 and 3, the colour developed decoloured rapidly ontreatment with the acidic solution.

EXAMPLE 4

100 parts cellulose acetate, 20 parts diethyl phthalate and 20 parts ofthe photographic film chemical “Color Developer CD3” were dissolved inacetone.

Film was cast and dried using the process described in Example 1, butinjecting only half the amount of dyestuff-containing solution, so thatthe composition of the film produced was

82.5% cellulose acetate

16.5% diethyl phthalate

1.0% “Color Developer CD3”

The film was colourless.

The photographic film chemical “Yellow Coupler 2” was dissolved at 1% inan aqueous acetone solution of hydrogen peroxide buffered to pH9. Whenthe film was marked with this solution, a bright yellow colour rapidlydeveloped.

What is claimed is:
 1. A process for testing the authenticity ofpackaged goods, comprising the steps of: packaging the goods inpackaging material including an outer layer of plastics film over atleast a part of a surface area of the packaged good, the plastics filmhaving a dyestuff dispersed in the body of the plastics film, saiddyestuff undergoing a clearly visible colour change when contacted witha colour-developing chemical, and applying to the outer layer of thepackaging material, which is comprised of the plastics film, saidcolour-developing chemical to produce a coloured marked area thereon toauthenticate the packaged good.
 2. The process according to claim 1,wherein the said plastics film forms the outermost layer of laminatedpackaging material.
 3. The process according to claim 1, wherein theplastics film forms a seal which has to be broken to open the package.4. The process according to claim 1, further comprising the step ofcontacting said marked area with a chemical which reacts with thedyestuff to change said marked area back to its original colour so thatthe marked area is indistinguishable from the rest of the film.
 5. Theprocess according to claim 1, wherein the dyestuff dispersed in the bodyof the plastics film is a latent dyestuff which is colourless andinvisible to the eye under ambient conditions for use of the film.
 6. Aplastics film and marker combination for identifying packaged goods towhich the plastics film is applied over at least a part of a surfacearea of the packaged good, comprising: a plastics film having a dyestuffdispersed in a body of the plastics film, the dyestuff undergoing aclearly visible colour change when contacted with a colour-developingchemical, and means for marking the plastics film with saidcolour-developing chemical to authenticate the identification of thepackaged good.
 7. The plastics film and marker combination according toclaim 6, wherein the dyestuff dispersed in the body of the plastics filmis a latent dyestuff which is colourless and invisible to the eye underambient conditions for use of the film.
 8. The plastics film and markercombination according to claim 6, wherein the plastics film is an outerlayer of a packaging material for packaging goods.
 9. The plastics filmand marker combination according to claim 6, wherein the plastics filmis an outer layer of a laminated packaging material for packaging goods.10. The plastics film and marker combination according to claim 6,wherein the plastics film comprises a seal for packaged goods.
 11. Theplastics film and marker combination according to claim 6, wherein theplastics film is a label for packaged goods.
 12. The plastics film andmarker combination according to claim 6, wherein the colour-developingchemical used to mark the plastics film is in solution in a solventwhich does not damage the plastics film.
 13. The plastics film andmarker combination according to claim 12, wherein said means for markingis a marker pen.
 14. The plastics film and marker combination accordingto claim 13, wherein said marker pen is a fibre-tipped pen.
 15. Theplastics film and marker combination according to claim 6, furthercomprising means for contacting a marked area of the plastic film with achemical which reacts with the dyestuff to change the marked area backto its original colour so that the marked area is distinguishable fromthe rest of the plastics film.